The present invention relates generally to multichannel fiber optical power monitoring apparatus, and more particularly, is directed to a switched multichannel fiber optical power monitoring apparatus.
It is known to tap an optical fiber in order to detect and measure the optical signal carried by the optical fiber. In such case, it is important that only a small percentage of the incoming light signal, that is, a small percentage of the optical power, be utilized for such detection and measurement. Such detection and measurement is useful, for example, to indicate the system performance, and is also used for maintenance and control of the optical line.
Conventionally, a fiber optic tap is placed in the optical path to extract a small fraction of the optical power from the optical path. This can be provided by a tap which then supplies the optical signal to a photodiode which converts the optical signal to an electrical signal. With such arrangement, there is low optical line loss and low polarization dependent loss (PDL). The electrical signal is then supplied to a micro-controller through a logarithmic amplifier.
However, in many instances, a plurality of optical paths or channels must be monitored. In such case, conventional practice provides a tap photodiode for each optical path, with a logarithmic amplifier connected to the output of each photodiode. Because an amplifier is provided for each photodiode, there is an increased cost due to a large number of parts, and an increased size in the circuitry.
Accordingly, it is an object of the present invention to provide a switched multichannel fiber optic power monitoring apparatus that overcomes the problems with the aforementioned prior art.
It is another object of the present invention to provide a switched multichannel fiber optic power monitoring apparatus which is greatly reduced in size.
It is still another object of the present invention to provide a switched multichannel fiber optic power monitoring apparatus which is greatly reduced in cost.
It is yet another object of the present invention to provide a switched multichannel fiber optic power monitoring apparatus which imparts a smaller amount of noise into the electrical signal.
It is a further object of the present invention to provide a switched multichannel fiber optical power monitoring apparatus which can easily control the switching times for the different channels to account for low light and other situations.
It is a still further object of the present invention to provide a switched multichannel fiber optic power monitoring apparatus that is easy and economical to use and manufacture.
In accordance with an aspect of the present invention, a switched multichannel fiber optic power monitoring apparatus, includes a plurality of photodetectors, each connected to a different optical line for converting an optical signal from the respective optical line to an electrical signal. There is at least one switch, the number of switches being less than the number of photodetectors, each switch having inputs connected to outputs of each of a plurality of the photodetectors for receiving the output electrical signal from each of the photodetectors and for switching the output electrical signals in a multiplexed manner to an output thereof as a multiplexed electrical signal. At least one amplifier is provided for amplifying the multiplexed electrical signal, the number of amplifiers being less than the number of photodetectors. An analog to digital converter converts the amplified electrical signal to a digital signal, and a microprocessor provides an output measurement signal in response to the digital signal.
The microprocessor is connected to the switch to control a length of time that the at least one switch is open for each optical line, and is connected with the at least one amplifier to control amplification by the amplifier. Preferably, each amplifier includes a logarithmic amplifier, and each photodetector is an integrated photodetector.
In one embodiment, each photodetector is connected to a tap of one of the optical lines for converting the optical signal from the respective optical line to the electrical signal, and in another embodiment, each photodetector receives the entire signal from one of the optical lines.
In accordance with a further embodiment of the present invention, the at least one switch includes a plurality of first switches and a second switch. Each of the first switches has inputs connected to outputs of each of a plurality of the photodetectors for receiving the output electrical signal from each of the photodetectors and for switching the output electrical signals in a multiplexed manner to an output thereof as a first multiplexed electrical signal, and the second switch has inputs connected to outputs of the first switches for switching the first multiplexed electrical signals in a multiplexed manner to an output thereof as a second multiplexed electrical signal which is supplied to the amplifier.
In accordance with a still further embodiment of the present invention, the at least one switch includes a plurality of switches, each having inputs connected to outputs of each of a plurality of the photodetectors for receiving the output electrical signal from each of the photodetectors and for switching the output electrical signals in a multiplexed manner to an output thereof as a first multiplexed electrical signal, and the at least one amplifier includes a plurality of amplifiers, each amplifier having an input connected with an input of a respective one of the switches. As one aspect thereof, outputs from the amplifiers are supplied directly to the microprocessor, while according to a modification, a further switch is provided having inputs connected to outputs of each of the amplifiers and for switching output signals from the amplifiers in a multiplexed manner to the microprocessor.
Preferably, the output measurement signal is a calibrated signal which is calibrated with respect to at least one of the following: temperature; input optical level; input optical wavelength and polarizations; and device parameters of the photodetectors, each switch, each amplifier, the analog to digital converter and the microprocessor.
The above and other objects, features and advantages of the invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.